Process of separating hydrocarbon mixtures



May 2l, 1940,. A c. E. ANDREWS erf.

PnocEss oF SEPAHATING HYRQCARBON uIxTUnEs Fiiea oct. 22. A193:3

Patented May 2l', v

PROCESS QF SEPARATING HYDROCARBON TUBES chester Andrews, Overbrookl and Merreii n.' Fenske, State College, Pa., assiznors to Rohm & Haas Company, Philadelphia, Pa.

Application October 22, 19381,. Serial No. 236,414

6 Claims. (Cl. 196-13) This invention relates to a process of separat ing mixtures of hydrocarbons, such as petroleum fractions, into fractions of different molecular type and different molecular size. More particularly it relates to a process of extracting such hydrocarbon mixtures in successive stages, employing in each'stage a methylamine solvent having a greater dissolving capacity than the solvent used in the preceding stage.

our copending application Serial No; 155,432 iiled July 24, 1937, which in turn is a continuation-in-part of our Patent No. 2,096,725 granted October 26, 1937.

Petroleum and the various fractions that are commonly obtainedfrom it by distillation consist essentially of yhydrocarbons of different mole-` cular type and different molecular weight. 'I'he different types of hydrocarbons present in such mixtures may be classified generally into three classes. There are the more highly polar types or aromatics, the cycloalphatics or naphthenes, and the aliphatics or paraffines.- Most petroleum oils and theirordinary fractions contain twoof these types and many of them contain all three.

There may also be present compounds, containing groups belonging to any two or all three of these classes but such compounds can generally be classifiedr in accordance with the properties of the predominating group. Within each of these groups there are compounds of different molecular weights and which have different solubilities in the solvents employed in the present invention. Generally speaking, the compounds of low molecular vweight in any group are more soluble than those of high molecular weight.

For a given molecular weight the aromatic com-- pounds are in general the most soluble and the paraflinic compounds the least soluble in any given solvent, the naphthenic compounds having an intermediate solubility.

The presentinvention is based on these varying solubilityl characteristics and on the fact that the dissolving capacity of the methylamine-solvents employed can be varied at will over a wide range so that they are adaptable to practically any conditions it is desired to impose onv the extraction process. A These `conditions comprise solvent to oil ratio, temperature, temperature gradient, and the type of extraction apparatus, i. e. wheth er it is a countercurrent tower ora series of mixers and settlers.

The dissolving capacity of the methylamine solvent ,caribevaried by changing its composition or by Achanging the temperature.. 'I'he three methylamines have differentdissolving capacity for hydrocarbons. Trimethylamine is the strongest vsolvent for.- nearly all hydrocarbons, dimethylamine next. and monomethylamine the weakest. Therefore by `employing various mix- This application is a continuation-impart of tures of two or all three of the methylamines the dissolving capacity of the solvent `can be varied over a rather wide range. This rangey mayv be p extended in the direction of lower dissolving capacity by mixing with the methylamine a liquid, miscible therewith, which has a lower capacity for dissolving hydrocarbons. The methylamines may then be'considered a primary solvent in which various amounts of a modifying solvent are dissolved. These modifying solvents are chemically inert toward the methylamines, are soluble in them, and possess a lower dissolving capacity for va particular hydrocarbon type than the methylamines. In the case of themethylamines these modifying solvents areA one or more of the following substances: molecular weight alcohols, the lower aliphatic cyanides, water, ammonia, ethers, and etheralcohols such as polyglycols andthe 4monoalkylethers of polyglycols. Of these the lower alcohols such as methanol and ethanol are particu- 16- methanol and the low y larly useful in the present invention. Methanol n is a suitable liquid because of its low solvent power, ease of separation from the oils, low viscosity of its mixtures with the methylamines andv ease of separation from the methylamines and recombination therewith to form any desiredsolvent mixture.. "I'hus, in extracting a heavyA petroleum oil, for'example, the first solvent used would contain Aa larger proportion of methanol than the second one which in turn would contain ,p

more methanol than the third solvent.

The ratio of solvent to oil may also Ava'rywidely and will depend on the nature of the oil, the proportion of the various constituents thereof, and I l the sizeof the fraction to be separated. The

ratio may vary between one and ten volumes of Y solvent per volume of oil being rtreated For most practical operations, however, the ratiowill be between two and four volumes of solvent per volume of oil. When successive extractions arev carried out on the oil by solvents of graduated*- vdissolving capacity; the ratio of solvent to oil may or may not be the saine in each stephthe actualf lratio chosen being determined' by various factors such as type of material being extracted, the proportion thereof in the oil and the solvent capacity of the solvent.

specific y The primary object of the present invention is to provide a continuous process in which the oil to be treated is brought into contact with successive solvent mixtures containing methylamine,l the dissolving capacity of leach solvent vmixture being greater than that of the one preceding it.v

2,037,319 and 2,052,971.

in the nal or strongest solvent mixture. Thus starting with a viscous petroleum fractions, for example. the dissolving capacity of the iirst solvent is adjusted so that it dissolves principally the aromatic compounds, the second solvent so that it dissolves principally the cycloparaiines and the third solvent so that it dissolves principally those hydrocarbons in the remaining mixture which have the lower molecular weights. There is, of course, no sharp line of demarcation between the solubilities of the various types and, since in all types the compounds of less molecular weight are more soluble than those of high molecular weight, there is bound to be some overlapping of solubilities,

The process is carried out in general as follows: The hydrocarbon mixture enters at a point between the top and bottom of a tower wherein it is brought in contact with the solvent which enters at the bottom when the solvent is lighter than the oil undergoing extraction. 'I'he tower may be of any suitable construction such, for example, asare shown in U. S. Patent 2,037,318; However, it should be understood that while towers Y have been illustrated, other phase contacting means, such as a series of mixers and settlers, are applicable. In the ilrst of a series of such towers the solvent chosen is one having a relatively low solvent capacity for the hydrocarbons and thus it can dissolve only the most easily soluble constituents of the oil. The solvent for purposes of illustration,

,i is speciiically lighter than the' oil and methanol is selected as the modifying solvent. Consequently the solvent rises in the tower countercurrent to the oil which naturally flows downward. As the solvent passes through the oil, it extracts the more readily soluble constituents and the solution thus formed passes out at the top of the tower and is conducted to a still where the solvent is removed asa vapor. The vapor is then led to a fractionating column in which the methanol and methylamine are separated. Part of the extract remaining in the still is returned to the top of the tower to assist in the separation oi' the constituents of the original oil. 'I'he remainder of the extract is removed from the system. It contains the major part of the aromatic constituents of the original oil along with small amounts of the other less soluble material.

Other means may also be employed for separating the solvent and the extract. As the solution l'eaves the top of the extracting column, it may be led into a cooling device. The temperature of the solution is then lowered to a point at which some of the extract precipitates. Two phases are thus formed, the lighter one being rich in solvent, the heavier containing mostly material extracted from the oil. The solution phase then goes to the still where the solvent is removed and the residue removed from the system. The heavier phase is returned to the top of the extraction tower where it acts as a reilux. It extracts the less soluble components from the counterowing solvent phase so that as the solvent phase flows toward the point where it leaves the extracting column the concentration of more soluble components in the solvent increases. Alternatively the solution leaving the extraction column may be mixed with a precipitant such as methanol. This precipitates the dissolved material in whole or in part according to the proportion of precipitant added. In genalready described. Part of the precipitate is then returned to the top of the extraction column to extract countercurrently the solvent phase, and the remainder removed from the system. The solvent goes to the still where it is separated from any residual extract which is removed from the system, the vapor of solvent being led to the fractionating column where it is resolved into its components. In all cases the separation of solvent and extract is complete and part of the extract is returned to the extracting column where it acts as a reflux.

'I'he oil phase which reaches the bottom oi.' the tower is substantially free of aromatic compounds. It is removed from the bottom of the tower and conducted to a point intermediate the ends of a second tower where it meets a rising current of fresh solvent which has a higher dissolving capacity than had the solvent used in the rst column. This solvent extracts more material from the oil, which in this case may be mostly cycloparaillnic compounds, and the solution thus formed passes out at the top of the column where it is treated according to any one of the methods described in connection with the operation of the first extraction column.

The oil phase which has now been subjected to two'extractions is withdrawn from the bottom of the second tower and passed into a third tower at a point intermediate the ends where it meets an ascending current of a solvent having a greater dissolving capacity than the one used in the second column. Here the operations described for the rst two towers are repeated. The extract probably contains some naphthenic hydrocarbons and some aliphatic ones having a lower molecular weight than those in the oil which passes out at the bottom ot the tower and which consists predominantly oi.' the aliphatic hydrocarbons having the highest molecular weight of those which were present in the original oil.

The original oil is thus separated into iour fractions, three extracts and one railinate, consisting essentially of aromatics in the rst exc tract, cycloaliphatics in the second, low molecular weight aliphatics in the third and the highest molecular weight aliphatics in the railinate. If further fractionation is desired, other towers operating as described above may be added to the system. Of course, the dissolving capacity of the extracting liquid used in each column will always be greater than that used in the preceding tower. The point where the oilis fed to the extraction tower, or feedpoint, is such that the composition of the oil in the tower corresponds as near as possible to that being fed to r the tower.

The process may be carried out in any suitable apparatus, a convenient arrangement of whichis shown diagrammatically in the accompanying drawing.l

The apparatus consists of three extracting units arranged in series. Each unit consists of a tower 2 equipped with inlets 3 for the material to be tracted and l for the solvent and outlets 5 and B for the raiinate and extract respectively. Pipe 1 equipped with valve 8 leads from outlet 6 to still 9 in the bottom of which is a heater III. Line II equipped with valve I2 leads from the bottom of the still and is connected through line I3 equipped with valve I4 to the top of tower 2. Connected with the line 'I is line I5 equipped with valve 49 which leads to separator I6 which is equipped with cooling coil I1. Line I8 equipped with valve I9 connects the bottom of the separator with line I3. Line equipped with valve l2|"connects the upper part of the separator with line 1. Line 22 equipped with valve' 23 leads from the top ofthe still to point 24 in fractionating column 25. From the top of the fractionating column pipe 26 leads to reilux condenser 21, from the bottom of which pipe 28 equipped with valve 23 leads to receiver 30. Line 3| equipped with valve 32 connects the line 28 with the upper part of the fractionating column. From the bottom of the receiver line 33 equipped with valve 34 leads through pump 35 to mixer 36. Fractionating column 25 is equipped with a heater 31. From the bottom of this tower line 38 erjiipped with valve 33 leads into receiver 40. From the bottom of receiver 4D linev 4| equipped with valve 42 leads through pump 43 to mixer 36. This mixer is connected with the bottom of the extraction tower 2 at inlet 4 by means of pipe 44. Line 45 equipped with valve 46 connects line 4| with line 1 at point between outlet 6 and valve 8.

The second and third units are constructed in the same manner, corresponding parts being designated by the same reference numbers to which are added prime or double prime marks to indicate the unit to which they belong.V

Line 41, 41 equipped with valves 48, 48 co nect outlets 5,-' with the inlets 3', 3" of't e extracting towers 2', 2". Line 41" equipped with valve 48" is connected with outlet 5" of extracting tower 2". I

The operation of this apparatus' will be described using, for purposes of illustration only, a heavy Pennsylvania residual oil as the mixture of hydrocarbons to be extracted and various mixtures of methylamine and. methanol as the sol.

vent. The methylamine is stored in receiver 3|I` and the methanol in receiver 48, from which they may be pumped in the proper proportions through metering pumps 35 and 43 into the mixer 36.

i The mixed solvent thus prepared enters the column 2 at inlet 4 where it meets ay descending body of oil which has been introduced through inlet 3. The oil, being specifically heavier than the solvent, passes down throughl the solvent and the solvent passes up through the oil dissolving the more readily soluble constituents of the oil. The extract phase thus formed passes out through line 1 and valve 8 into still 9, valves 46, 49, 2| and I3 being closed during this operation. The solution is then heated in the still so that the solvent is all evaporated and passes off through line 22 to the fractionating column 25. 'I'he residue left in the still is withdrawn through pipe II, valves I2 and I4 being' adjusted so that part of the residue passes out of the system through valve I2 and the remainder returns to ythe top of tower 2 through line I3. In this manner part of the extract may be used as a reflux to assist in separating the constituents of the oil being extracted. In stead of passing the extract phase directlyA into the still it may first be passed through the separator I6 where it is cooled by means of cooling coil I1 to such a degree that part atleast of the extracted material precipitates. 'In this operation valves 48 and 8 are closed and I4, 43, I9 and 2| are open. This precipitate is led through line I8 into line I3 where part of it may be returned to the top of column 2 and part withdrawn through valve I2, valve I4 being adjusted so as to regulate the amounts of extract returning to the column and of that withdrawn from the system. The solution phase formedin separator I6 passes through line 20 into line 1 and thence'into the still 9 where the solvent is removed and the residue withdrawn as described above. f

Instead of reducing the temperature of the extract phase to precipitate part of theextract, this may be accomplished by adding a precipitant, for example methanol, to the extract phase. This may be done by pumping methanol through line 45 and valve 45 into line 1, valve 8 being closed, and thence into the separator I6. The precipitate and solvent phases thus formed are treated in the manner described above.

'Ihe ralnate passing downwards in extraction column 2 is led by means of pipe 41 to the inlet 3' of extraction column 2 and fresh solvent of higher solvent capacity than that used in column 2 enters at inlet 4' and rises through the column. The extract phase' leaves the top of the column at outlet 6' and may then be treated in any one of the three ways described in connection with the operation of extraction column 2. The raffinate from column 2' is then led through line 41' to inlet 3" of column 2" where the operation of the extraction tower 2' is repeated, fresh solvent of higher solvent capacity than that in column 2' entering this column at 4". The inal rainate is withdrawn from column 2" through v line 41" and valve 48". 'Ihe solvent vapors distilled from stills 3, 9', 3" are conducted to the fractionating column through lines 22, 22', 22" respectively. Here the mixture of methanol and `methylamine is fractionated, the methylamine being collected inf receiver and the methanol vin receiver 40.

In this manner the oil isseparated into four fractions, three extracts and one railnate. The extracts are removed from the system through valves I2, I2', I2" and the nal rafllnate through valve 48".

As mentioned above, an oil of the type indicated above generally contains three classes of .compounds, aromatic, hydro-aromatic or naphthenic, and aliphatic. The aromatic compounds are the most readily soluble and are, therefore, extracted with the weakest solvent in column 2. The hydroaromatic or naphthenic are less soluble and, therefore, a stronger solvent such as used in column 2' is necessary.to'extract them.k The oil entering column!" consists principally of laliphatic compounds and is separated into 4twovaliphatic fractions, one of 'high molecular `weight which is the'raillnate'and one of lower molecular weight which yis the extract. Q

A Pennsylvania ABright Stock wasextracted in the foregoing manner and separated in to four fractions, The'solvent mixture employed in the first unit contained 75% technical monomethylamine and 25% methanol. In the second unit an 85/15 mixture was used and in the third a 95/5 mixture. The following table gives the viscosity characteristics of the three extracts and the rafnate in comparison withthose of theoriginal oil.

It is seen from these results that the most soluble fraction, Extract #1, contains compounds, probably mostly of aromatic nature, which have'a low viscosity index. 'I'he next fraction has a higher viscosity index but still not the equal of that of the original oil. The thirdextract has a viscosity index somewhat greater than that of the original bright stock and probably contains a large proportion of the lower molecular weight aliphatic hydrocarbonsoriginally present. The railinate is an oil of very high viscosity having a viscosity index considerably higher than that of the starting material.. It probably consists'almost entirely of the high molecular weight aliphatic hydrocarbons.

In carrying out the process the entire system is kept under pressure which is determined principally by the temperature at which the extractions are performed. `This pressure is usually great enough to condense the methylamines at ordinary temperature so that no refrigeration or extra cold cooling water is required in the condenser.

The temperature of the extraction steps may be varied to suit conditions. It is advantageous, however, to have the temperature of the liquid at the bottom of the extraction towers somewhat higher than that at the top. More particularly, it is desirable to have a drop in temperature in the direction of solvent ilow. 'I'he temperature drop through the tower may be as much as 100 to 200 F. if desired, and can be regulated by adjusting the temperature of the incoming oil and solvent, as well as by suitably arranged heating and cooling units. It is. also advantageous to operate at a somewhat elevated tempera'ture, say 10o-170 F. Aht the higher temperatures the viscosity of the liquids is considerably reduced which facilitates the flow through the system and favors more efficient extraction. It is also of advantage to Ahave a fairly high temperature when using the procedure according to which part of the extract is precipitated in the separators i6 by cooling. Thus, by being able to adiust the dissolving power of the methylamine solvent by the modifying solvent, it is possible to' have optimum conditions for extraction. With ordinary extraction solvents, the dissolving power of the solvent may only be adjusted by temperatures, but in so doing other factors are simultaneously affected, frequently in an undesirable way.

It is often advantageous to mix the oil to be extracted with lighter, less viscous paraillnic type hydrocarbons, particularly the lower petroleum fractions such as naphtha or kerosene which can subsequently be removed from the railinate by evaporation at relative low temperatures. This is particularly advantageous in treating very viscous oils or oils which on extraction yield fractions of very high viscosity. The lighter hydrocarbon reduces the vicosity of the heavy oil, thus facilitating its iiow through the system and making it more easily accessible to the action of the methylamine solvent. The amount of light hydrocarbon added can be varied over a rather wide range, for example from 1 to 3 volumes of diluent to 10 volumes of oil. The actual amount used will naturally depend on the properties of the oil being treated, the desired reduction in viscosity and the composition of the solvent being used.

' The diluent may be added before the oil enters the extractiony system or at a later stage. For example, if the initial oil is not very viscous and can be treated Without dilution in the first tower but yields a very viscous raiinate in the second tower, the diluent may be added as the oil enters the third tower. Of course, if conditions require, it may be mixed with the oil entering the second tower.

For extracting materials of low viscosity and low molecular weight such as gasolines, methylamine-water solutions are enective solvents. In some cases these solvents may be heavier, rather 'f than lighter, than the mixture being extracted.

solutions whether the solvent is lighter or heavier than the hydrocarbon mixture being extracted.

We claim: l

1. The process of separating mixtures of hydrocarbons containing molecules of different types and weights, which comprises treating said mixture with a solvent composed of at least one methylamine and a modifying solvent, the dissolving capacity of said solvent being so adjusted that it dissolves predominantly aromatic hydrocarbons, separating an extract and a railinate, treating said rafiinate with a second solvent composed of at least one methylamine and a modifying solvent but containing a greater proportion of methylamine than the iirst solvent and being capable of dissolving predominantly naphthenic hydrocarbons, separating a second extract and a second raffinate, treating said second raillnate with a solvent composed of at least one methylamine and a modifying solvent but containing a -greater proportion of methylamine than thesecond solvent and being capable of dissolving predominantly parafllnic hydrocarbons of lower molecular weight range, separating a third extract and a third raiiinate which contains predominantly parailinic hydrocarbons of higher molecular weight range.

2.' The process of separating mixtures of hydrocarbons which contain molecules of different types and weights, which comprises treating said mixture with a solvent composed of at least one methylamine and methanol, the dissolving capacity of said solvent being so adjusted that it dissolves predominantly aromatic hydrocarbons, separating an extract and a railinate, treating said raflinate with a second solvent composed of at least one methylamine and methanol but containing a greater proportion of methylamine than the'first solvent and being capable of dissolving predominantly naphthenic hydrocarbons, separating a second extract and a second railinate, treating said second railinate with a solvent composed of at least one methylamine and methanol but containing a greater proportion of methylamine than the second solvent and being capable of dissolving predominantly paranic hydrocarbons of lower molecular weight range, separating a third extract and a third railinate which contains predominantly parailnic hydrocarbons of higher molecular weight range.

3. The process of separating mixtures of hydrocarbons which contain molecules of different.

types and weights, which comprises treating said mixture with a solvent composed of at least one methylamine and ammonia, the dissolving capacity of said solvent being so adjusted that it dissolves predominantly aromatic hydrocarbons, separating an extract and a raflinate, treating' said raffinate with a second solvent composed of at least one methylamine and ammonia but containing a greater proportion of methylamine than the iirst solvent and being capable of dissolving predominantly naphthenic hydrocarbons, separating a second extract and a second rafiinite, treating said second raffinate with a solvent composed of at least one methylamine and ammonia l but containing a greater proportion of methylamine than the second solvent and being capable of dissolving predominantly parainic hydrocarbons of lower molecular weight range, separating a third extract and a third raffinate which contains predominantly paraiiinic hydrocarbons of high molecular range.

4. The process of separating a heavy lubricating oil into fractions, which comprises treating the oll with a solvent containing about 75% of the monomethylamine and about 25% of a modifying solvent, said solvent being capable of dissolving predominantly the armatic hydrocarbons contained in said oil, separating an extract and a raiilnate, treating the raflinate with a second solvent containing about 85% of monomethylamine and about 15% of a modifying solvent, said second solvent being capable of dissolving predominantly naphthenic hydrocarbons, separating a second extract and a second raffinate, treating said second raffinate with a third solvent containing about 95% of monomethylamine and about of a modifying solvent, said third solvent being capable of dissolving predominantly parafflnic hydrocarbons of lower molecular weight range, separating a final extract and a nal rafflnate which contains predominantly paraftlnic hydrocarbons of higher molecular weight range.

5. The process of separating a heavy lubricating oil into fractions, which comprises treating the oil with ,a solvent containing about r% of monomethylamine and about 25% of methanol which is capable of dissolving predominantly the aromatic hydrocarbons contained in said oil, separating an extract and a raiiinate, treating the raflinate with a second solvent containing about 85% of monomethylamine and about 15% of methanol capable of dissolving predominantly naphthenic hydrocarbons, separating a second extract and a second raiiinate, treating said second railnate with a third solvent containing about 95% of monomethylamine and about 5% of methanol capable of dissolving predominantly parafnic hydrocarbons of lower molecular Weight range, separating a final extract and a final raffinate which contains predominantly paraflnic hydrocarbons of higher molecular weight range.

6. The process of separating mixtures of hydrocarbons containing molecules of diierent types and sizes, which comprises treating said mixture in stages with a series of solvents composed of at least one methylamine and a modifying solvent, separating an extract and a raiilnate in each stage and treating each rainate with one of said series of solvents containing a greater proportion of methylamine than the solvent employed in the preceding stage, the dissolving capacities of the solvents being so adjusted that the lirst ones dissolve predominantly aromatic hydrocarbons, the intermediate ones predominantly naphthenic hydrocarbons, and the nal ones predominantly paramnic hydrocarbons of lower molecular weight range.

CHESTER E. ANDREWS. MERRELL R. FENSKE. 

